Per face vertex coloring
Adjacent faces can have different plain colors, and a vertex can have a different color for each face it participates to.

In 2.79, it's possible to select the faces in Vertex Paint mode, and use 'Set Vertex Colors' (Header > Paint menu or Shift-K).

  

Likely the integration in Blender of a separate script that was used before.

Edit:


To view colors in the 3D editor when 'Material' display mode is selected, the option 'Vertex Color Paint' must be enabled for the material used (Properties editor > Material tab > Options panel).
The 'Face Selection Masking for Painting' button must be down in the 3D Editor header (Vertex Paint mode).